1. Field of the Invention
The present general inventive concept relates to a stereo sound generation apparatus, and more particularly, to a stereo sound generation method and apparatus to generate a stereo sound, by using 2-channel headphones, earphones, or speakers, from a multi-channel sound signal reproduced through a variety of media such as a DVD-video, and a DVD-audio.
2. Description of the Related Art
Recently, a technology allowing a user to listen to 3D stereo sound with only headphones without speakers supporting 5.1 channels has been and is being implemented.
A home theater system outputs sounds through 5 speakers. However, these sounds do not always arrive directly at the ears of a listener, but part of these sounds is reflected by walls or furniture in a room and then arrives at the listeners ears. When all sound signals arrive at the listeners ears, the brain receives all these sound signals and senses the sound signals as a stereo sound.
In order to implement this stereo sound only with ordinary headphones, a stereo sound generation system based on a processor coding audio information has been and is being developed.
A technology related to this stereo sound generation system is disclosed in WO 99/49574 (PCT/AU99/00002, filed 6 Jan. 1999, entitled, “AUDIO SIGNAL PROCESSING METHOD AND APPARATUS”).
In the technology related to the conventional stereo sound generation system, a multi-channel audio signal is down-mixed into a 2-channel audio signal by using a head related transfer function (HRTF).
Referring to FIG. 1, a 5.1-channel audio signal is input. The 5.1 channels include a left front channel 2, a right front channel, a center front channel, a left surround channel, a right surround channel, and a low frequency effect (LFE) channel. In each channel, an impulse response function relative to the left ear and right ear of a listener is applied. Accordingly, in relation to the left front channel 2, the impulse response function 4 of the left ear corresponding to the left front channel signal is convoluted with a left front channel signal 3. The impulse response function 4 of the left ear relative to the left front channel signal 3 uses a HRTF as an impulse response to be received by the left ear as an ideal spike output from a left front channel speaker placed at an ideal position. An output signal 7 is added to a left channel signal 10. Similarly, in order to generate an output signal 9 to be added to a right channel signal 11, an impulse response function 5 of the right ear relative to the left front channel signal 3 is convoluted with the left front channel signal 3. Accordingly, the arrangement of FIG. 1 requires approximately 12 convolution operations in relation to the 5.1 channel signals. As a result, by down-mixing the 5.1 channel signals to a 2-channel signal by combining the measured HRTFs, the same surround effect as when a multi-channel signal is reproduced can be achieved.
However, though the system of FIG. 1 provides a stereo effect by localizing a plurality of virtual sound sources, it does not generate reflected sounds to create a spatial effect that can be felt by the listener.